This invention generally relates to spin coating system and more particularly to a dual cup spin coating system for capturing a flowable spin coating material discharged from a process substrate surface.
In the manufacturing processes for integrated circuits, photolithography process, for example, is frequently used for forming features of a semiconductor device on a semiconductor process wafer. The photolithography process generally involves applying a layer of photoresist to the process wafer surface followed by exposure to an activating light source through a mask defining device feature patterns. After development of the exposed photoresist, the photoresist provides, for example, an etching pattern for forming the device feature.
In many cases, the photoresist is applied according to a spin coating process whereby an amount of flowable photoresist is applied to a process surface of the semiconductor process wafer while the process wafer is spinning. The flowable photoresist is distributed over the surface according to centrifugal forces, a portion of the flowable photoresist being discharged of the edge of the semiconductor process wafer into a collecting cup.
Generally, the spin coating system used to apply the flowable photoresist includes a rotatable wafer support platform housed in an ambient controlled chamber. The process wafer adheres to the surface of the wafer support chuck by means of a vacuum force typically applied to a central portion of the wafer support platform by means of a vacuum. In operation, typically an O-ring sealing means is disposed on surface of the wafer support platform (vacuum chuck) to form a vacuum seal around the central portion of the non-process surface (back) of the process wafer to maintain a vacuum suction force to hold the process wafer firmly in place while the wafer support platform is rotated at high speeds.
In a typical spin coating process, an amount of flowable coating material, for example, photoresist is applied to a central portion of the process wafer surface where centrifugal forces induced by the spinning wafer support platform cause the flowable coating material to evenly coat the wafer surface with a thin film of flowable coating material. In many cases, the spinning rate of the wafer support platform may be altered to achieve a more uniform or thinner coating. The spin rate of the wafer support platform is determined by factors such as the viscosity of the flowable coating material, the desired thickness of the flowable coating film, and the rate of solvent evaporation from the coating material.
A conventional spin coating system is shown in FIG. 1 in a cross sectional side view representation. The spin coating system 10, includes a drain cup 12 and a vacuum chuck 20 attached to rotatable shaft 32, a vacuum force being applied through rotatable shaft 32 to vacuum chuck 20 for rotating process wafer 26B held in adjacent relation to vacuum chuck 20 by means of the vacuum force. The drain cup 12 includes an outer cup 12A portion enclosing and surrounding the process wafer and having an inner face portion 14A disposed above the periphery of the process wafer circumferential edge designed to intercept flowable coating material discharged at a positive angle with respect to the process wafer surface 26A following for example, trajectories C1 and C2, thereby deflecting it into the drain region 16. The drain region 16 of the drain cup 12 is formed between the outer cup portion 12A and an inner cup portion 12B disposed below the peripheral portion of the process wafer. The drain region 16 is may optionally be supplied with a positive or negative air pressure source (not shown) for aiding the removal of the discharged flowable coating material through exhaust pathway 18.
In operation, the vacuum chuck 20 is rotated at a pre-determined rate causing process wafer 26B to spin at a predetermined rate while a flowable coating material dispenser (not shown) disposed above the central portion of the process wafer 26B dispenses a pre-determined amount of flowable coating material at a pre-determined rate. The flowable coating material is spread out from the central portion of the process wafer by centrifugal forces toward the circumference of process wafer 26B where excess flowable coating material is discharged off the circumferential edge of the process wafer 26B to be captured by drain cup 12 in drain region 16 and subsequently removed.
One problem with the prior art spin coating system is the collection of back spattered coating material onto the process wafer surface. In typical operation, as the flowable coating material is discharged off the circumferential edge of the process wafer, a certain portion, especially at higher speeds, for example 3000 to 4000 rpm, follows, for example, trajectory C3 impacting the inner face portion 14B of the drain cup 12. As a result of the impact, the flowable coating material is back spattered from inner face portion 14B and may follow, for example, trajectory A or B. Consequently, following for example, trajectory B, a portion of the back spattered material, frequently in particulate form, is deposited on the process wafer surface 26A, contaminating the surface and interfering with subsequent semiconductor wafer processing operations. For example, the contaminating particles can interfere with exposure and development of photoresist patterns thereby causing defects in critical dimensions of semiconductor device features.
Another shortcoming of the prior art spin coating system are discontinuities caused in the coating near the process wafer circumferential edge. According to the prior art drain cup 12, the upper portion of the outer cup portion 12A including inner face portion 14B, causes turbulence including the formation of eddy currents over the circumferential edge portion of the process wafer surface. As a result, that portion of flowable coating material discharge upward a positive angle to the process wafer surface is increased, thereby not only causing non-uniformities along the circumferential edge of the process wafer, but exacerbating the degree of particle contamination on the process wafer surface caused by discharged flowable coating material back spattering off the inner face portion 14B of the drain cup 12.
There is therefore a need in the semiconductor processing art to develop a spin coating system that more effectively captures discharged excess flowable coating material and that reduces the turbulence present around the circumferential edge of a process substrate thereby minimizing contamination of the substrate process surface and improving the coating uniformity at the circumferential edge of a process substrate.
It is therefore an object of the invention to provide to develop a spin coating system that more effectively captures discharged excess flowable coating material and that reduces the turbulence present around the circumferential edge of a process substrate thereby minimizing contamination of the substrate process surface and improving the coating uniformity at the circumferential edge of a process substrate while overcoming other shortcomings and deficiencies in the prior art.
To achieve the foregoing and other objects, and in accordance with the purposes of the present invention, as embodied and broadly described herein, the present invention provides a dual cup spin coating system for capturing a discharged flowable coating material in a spin coating process.
In a first embodiment according to the present invention, the dual cup spin coating system includes a first outer cup and a second outer cup said first outer cup concentrically disposed around the second outer cup forming a first capture space arranged for capturing at least a portion of a discharged flowable coating material discharged from a process substrate at a first positive angle with respect to the process substrate in a spin coating process; and, an inner cup disposed concentrically within the second outer cup forming a second capture space arranged for capturing at least a second portion of the discharged flowable coating material discharged from the process substrate at a second positive angle less than about the first positive angle with respect to the process substrate in a spin coating process.
In another embodiment, at least the first outer cup and second outer cup respectively form a first and second intercept surface wherein a perpendicular thereto forms an intercept angle of between about 0 degrees and about 90 degrees with respect to the process substrate surface for capturing at least a portion of the discharged flowable coating material.
In another embodiment, the second capture space includes a first exhaust pathway for removing the discharged flowable coating material. Further, the first capture space communicates with the second capture space by means of at least one second exhaust pathway for removing the discharged flowable coating material. Further yet, the at least one second exhaust pathway further comprises at least one opening formed through the periphery of the second outer cup. Yet further, the at least one opening comprises a plurality of openings including at least one of a circular, right circular, and polygonal shape.
In another embodiment, the first and second outer cups include coupling means for coupling to a rotatable shaft for spinning the process substrate such that the rotatable shaft spins the at least the first and second outer cups synchronously with the process substrate.
In yet another embodiment, at least one of a vacuum chuck for mounting the process substrate and the dual cup spin coating system include means for adjusting a level of the process substrate with respect to at least the first and second outer cups.
In a further embodiment, at least a first notched region and second notched region are formed in the first and second intercept surfaces, respectively, extending circumferentially along the first and second intercept surfaces adjacent to a respective inner diameter of the first and second outer cups for reducing turbulence.
In another embodiment, the first capture space is arranged to capture about 15 to about 30 percent of the discharged flowable material and the second capture space is arranged to capture about 70 to about 85 percent of the discharged flowable material.
These and other embodiments, aspects and features of the invention will be better understood from a detailed description of the preferred embodiments of the invention which are further described below in conjunction with the accompanying Figures.